O'Brien's daughter is sent back in time and returns changed.
On a family picnic on the planet Golana, eight-year-old Molly O'Brien falls through an ancient time portal and is thrown 300 years into the past, onto a world that was then empty. The crew reopens the portal and transports her back, but the timing is off: the girl they recover is eighteen and feral, having survived alone for a decade. Miles and Keiko build her a habitat on the station and try to reach her, and Molly slowly begins to remember them.
When she becomes violent and injures a man, Starfleet plans to place her in an institution. With Odo's help, the O'Briens secretly return her to Golana. Going back through the portal, the older Molly meets her younger self just after the fall and sends her back home, and the adult Molly vanishes as history is restored. The seventh-season episode is an emotional study of the O'Briens as parents and of the bond between them and their daughter.